# Patent

## Title
Doxycycline metal complex in a solid dosage form

## Abstract

The present invention is a solid dosage form of a doxycycline metal complex. The present invention also includes a process for making a doxycycline metal complex in a solid dosage form. The process comprises the steps of (i) providing an aqueous solution of doxycycline or a physiologically acceptable salt thereof; (ii) admixing a metal salt with the aqueous solution; (iii) admixing a base to increase the pH of the aqueous solution, thereby forming a suspension of doxycycline metal; and (iv) drying the suspension, thereby forming a dry granulation of doxycycline metal complex.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of application Ser. No. 10/896,045, filed Jul. 22, 2004, which claims the benefit of U.S. Provisional Application No. 60/490,136, filed Jul. 25, 2003. The entire contents of all of the above mentioned applications are incorporated herein by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a doxycycline metal complex. More particularly, the present invention is directed to a solid dosage form of a doxycycline metal complex.
2. Related Background Art
Doxycycline (6-deoxy-5-hydroxytetracycline monohydrate) is a broad spectrum bacteriostatic compound that is effective against gram-positive, gram-negative, aerobic and anaerobic bacteria, as well as spirochetes, mycoplasmas, rickettsiae, chlamydiae and some protozoans. It works by inhibiting protein synthesis in bacteria or protozoans, which effectively kills them. It is commonly used in the treatment of bacterial infections caused by these organisms, such as urinary tract infections, upper respiratory tract infections, acne, gonorrhea, chlamydia, anthrax, lyme disease and others.
Individuals taking doxycycline, are advised that iron supplements, multivitamins, calcium supplements, antacids, or laxatives should be avoided. These products can adversely reduce the efficacy of doxycycline by reducing its absorption in the body.
British Patent No. 1,360,998 to Villax describes a process for isolation of α-6-deoxytetracyclines from a crude reaction mixture. The patent also discloses that calcium salts of tetracyclines are suitable for oral preparations such as suspensions. However, calcium salts of doxycycline are known to be particularly unstable in an alkaline pH environment. Moreover, the process described by Villax, uses an organic solvent, i.e., methanol. While organic solvents are often used to prepare pharmaceutically active ingredients, they are generally not desirable in the process of preparing a solid dosage form containing a pharmaceutically active ingredient. Clearly, the process disclosed in Villax for isolating the deoxytetracyclines would not result in a solid dosage form suitable for pharmaceutical administration to humans due to residual solvent.
Doxycycline is a very bitter tasting drug. Currently, a doxycycline metal salt is only available as a suspension of doxycycline calcium. An advantage of the doxycycline calcium complex suspension is that it has an acceptable taste. But many individual's find a liquid dosage form inconvenient. Having no real alternative, i.e., a solid dosage form of a doxycycline metal complex, they must put up with the inconvenience.
Another source of doxycycline is doxycycline hyclate. However, it can cause complications, such as esophageal ulceration. This would not be a problem with a solid dosage form of doxycycline. For example, a doxycycline calcium complex chewable tablet, if available, would not cause ulceration of the esophagus because the drug would not be soluble and therefore would pass through the esophageal environment without harming it.
However, making a solid dosage form of a doxycycline metal complex is extremely difficult. For example, it is not known how to filter a doxycycline metal complex in an aqueous suspension, such as doxycycline calcium complex. Prior art methods have not made it possible to obtain reasonably pure doxycycline metal complex from an aqueous solution.
SUMMARY OF THE INVENTION
The present invention is directed to a solid dosage form of a doxycycline metal complex for pharmaceutical administration.
The present invention includes a solid dosage form of a pharmaceutical composition comprising: (i) a doxycycline metal complex and (ii) one or more pharmaceutically acceptable excipients.
The present invention also includes a process for making a doxycycline metal complex in a solid dosage form. The process comprises the steps of (i) providing an aqueous solution of doxycycline or a physiologically acceptable salt thereof; (ii) admixing a metal salt with the aqueous solution; (iii) admixing a base to increase the pH of the aqueous solution, thereby forming a suspension of doxycycline metal; and (iv) drying the suspension, thereby forming a dry granulation of doxycycline metal complex. Optionally, the process may include the step of admixing one or more pharmaceutically acceptable excipients. The excipient may be added prior to the step of drying the suspension or after the doxycycline metal complex granulation is formed. Moreover, the granulation may be further processed by filling the granulation into capsules or compressing it into tablets.
In another embodiment, the process for making a doxycycline metal complex in a solid dosage form comprises the steps of (i) providing an aqueous solution of doxycycline or a physiologically acceptable salt thereof; (ii) admixing a metal salt with the aqueous solution; (iii) admixing a base to increase the pH of the aqueous solution, thereby forming a suspension of doxycycline metal complex; (iv) admixing one or more pharmaceutically acceptable-excipients with the suspension to absorb water, thereby forming a wet granulation; and (v) drying the wet granulation, thereby forming a dry granulation of doxycycline metal complex. Optionally, the step of admixing one or more pharmaceutically acceptable-excipients may be performed after the wet granulation is formed. In addition, the dry granulation may be further processed by filling the dry granulation into capsules or compressing it into tablets.
In yet another embodiment, the present invention is a method of treating bacterial infections, which comprises the step of administering a safe and effective amount of a doxycycline metal complex in a solid dosage form for an effective time period, to a host in need thereof.
In addition, the invention includes a method for treating ailments resulting from microorganisms and/or bacteria, comprising the step of administering a safe and effective amount of a doxycycline metal complex in a solid dosage form for an effective time period, to a host in need thereof.


DETAILED DESCRIPTION OF THE INVENTION
For the purposes of the present invention, all percentages given denote percent by weight, unless otherwise specified.
The doxycycline metal complex and the active ingredients of the present invention are used in a “safe and effective amount.” This is understood to mean a sufficient amount of a compound or composition that will positively modify the symptoms and/or condition to be treated, with the proviso that the amount is low enough to avoid serious side effects. The amount of the compound, e.g., doxycycline metal complex, that is considered safe and effective, will depend upon several factors. For example, one should consider the condition and severity of the condition being treated, the age, body weight, general health, sex, diet, and physical condition of the patient being treated, the duration of the treatment, the nature of concurrent therapy, the particular active ingredient being employed, the particular pharmaceutically-acceptable excipients utilized, the time of administration, method of administration, rate of excretion, drug combination, and any other relevant factors.
The term “pharmaceutically-acceptable excipient” is understood to mean any physiologically inert, pharmacologically inactive material known to one skilled in the art, which is compatible with the physical and chemical characteristics of the particular doxycycline metal complex selected for use.
The present invention is directed to a solid dosage form of a doxycycline metal complex for pharmaceutically acceptable administration to a human, i.e. any residual solvents or other impurities are at a level that is considered safe for human consumption. The doxycycline metal complex may be, for example, doxycycline calcium complex, doxycycline magnesium complex, doxycycline sodium complex, or doxycycline zinc complex. One advantage of the doxycycline metal complex is that it delivers to the user/patient, doxycycline and a mineral source which may be useful. For example, a doxycycline calcium complex tablet would provide the user/patient a source of doxycycline and a source of calcium.
This is contrary to the teachings of the prior art, where it is taught that calcium inhibits the absorption of tetracycline. The inventors, however, have discovered that a therapeutic amount of doxycycline can be absorbed from a doxycycline metal solid, e.g., doxycycline calcium complex in solid dosage form, as taught by the present invention.
Ideally, the doxycycline has undergone complete complexation. This is understood to mean that at least about 75% by weight of the doxycycline is complexed. More preferably at least about 90% has complexed. It should be understood, however, that an excess of doxycycline or metal salt may be added to form the doxycycline metal complex.
It has been hypothesized that the doxycycline metal complex has a metal to doxycycline mole ratio of from about 0.5 to about 3 in the solid dosage form. Preferably the ratio is from about 1.5 to about 2.5, and more preferably about 1:2.
The present invention also includes a pharmaceutical composition formulated together with pharmaceutically acceptable carriers or excipients and/or bioactive agents. The composition comprises (i) a doxycycline metal complex and (ii) one or more pharmaceutically-acceptable excipients.
Preferably, the pharmaceutical composition may take the form of a powder, capsule, tablet, coated tablet, aerosol, pellet, chewable tablet, lozenge, gelatin filled capsule, and the like.
Suitable pharmaceutically-acceptable excipients include, but are not limited to, polymers, resins, plasticizers, fillers, lubricants, binders, disintegrants, granulating agents, solvents, co-solvents, surfactants, preservatives, sweetening agents, flavoring agents, buffering systems, antioxidants, pharmaceutical grade dyes, pigments, and mixtures thereof.
Polymers that may be used, include but are not limited to, hydroxypropylmethylcellulose (HPMC) alone and/or in combination with hydroxypropylcellulose (HPC), carboxymethylcellulose, acrylic resins such as Eudragit®, methylcellulose, ethylcellulose, and polyvinylpyrrolidone or other commercially available film-coating preparations.
Suitable plasticizers, include but are not limited to, polyethylene glycol, propylene glycol, dibutyl phthalate, castor oil, acetylated monoglycerides, triacetin, and mixtures thereof.
Examples of fillers, include but are not limited to, lactose, sucrose, maltodextrin, mannitol, starch, microcrystalline cellulose, and mixtures thereof.
Lubricants that may be used, include but are not limited to, magnesium stearate, stearic acid, talc, and mixtures thereof.
Suitable binders, include but are not limited to, methycellulose, sodium carboxymethycellulose, hydroxypropylmethylcellulose, carbomer, povidone, acacia, guar gum, xanthan gum, tragacanth, calcium silicate, magnesium aluminum silicate, ethylcellulose, pregelatinized starch, and mixtures thereof. Particularly preferred are methycellulose, carbomer, xanthan gum, guar gum, povidone and sodium carboxymethycellulose.
Disintegrants that may be used, include but are not limited to, crospovidone, sodium carboxymethyl starch, sodium starch glycolate, sodium carboxymethyl cellulose, alginic acid, clays, ion exchange resins, and mixtures thereof.
Examples of surfactants, include but are not limited to, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene monoalkyl ethers, sucrose monoesters, lanolin esters and ethers, and mixtures thereof.
Suitable preservatives, include but are not limited to, phenol, alkyl esters of parahydroxybenzoic acid, benzoic acid and the salts thereof, boric acid and the salts thereof, sorbic acid and the salts thereof, chlorbutanol, benzyl alcohol, thimerosal, phenylmercuric acetate and nitrate, nitromersol, benzalkonium chloride, cetylpyridinium chloride, methyl paraben, propyl paraben, and mixtures thereof. Particularly preferred are the salts of benzoic acid, cetylpyridinium chloride, methyl paraben and propyl paraben.
Antioxidants that may be used, include but are not limited to, tocopherols and derivatives thereof, ascorbic acid, beta-carotene, selenium, sodium bisulfite, sodium metabisulfite, ascorbyl palmitate, and mixtures thereof.
Suitable sweeteners, include but are not limited to, sucrose, glucose, saccharin, aspartame, and mixtures thereof. Particularly preferred are sucrose and saccharin.
Buffering systems that may be used include, but are not limited to, potassium acetate, boric carbonic, phosphoric, succinic, malic, tartaric, citric, acetic, benzoic, lactic, glyceric, gluconic, glutaric, glutamic, and mixtures thereof. Particularly preferred are phosphoric, tartaric, citric, and potassium acetate.
Water is preferably used as the solvent. Although other solvents may be used.
Suitable co-solvents, include but are not limited to, ethanol, glycerin, propylene glycol, polyethylene glycol, and mixtures thereof.
The pharmaceutical compositions described herein are comprised of from about 0.1 weight percent (wt. %) to about 99.9 wt. %, preferably from about 5.0 wt. % to about 50.0 wt. %, and most preferably from about 10 wt. % to about 50 wt. % doxycycline metal complex, and from about 0.1 wt. % to about 99.9 wt. %, preferably from about 5.0 wt. % to about 99.9 wt. %, and most preferably from about 50 wt. % to about 90 wt. % of one or more pharmaceutically-acceptable excipients.
The solid dosage form of a doxycycline metal complex is made using a novel process. The process comprises the steps of (i) providing an aqueous solution of doxycycline or a physiologically acceptable salt thereof; (ii) admixing a metal salt to the aqueous solution, (iii) admixing a base to increase the pH of the aqueous solution, thereby forming a suspension of doxycycline metal complex; and (iv) drying the suspension, thereby forming a dry granulation of doxycycline metal complex. Optionally, one or more pharmaceutically acceptable-excipients may be admixed, before, during, or after each processing step.
The doxycycline or physiologically acceptable salt may be, for example, doxycycline hyclate, doxycycline monohydrate, doxycycline carrageenate, doxycycline phosphate, or mixtures thereof. The doxycycline or physiologically acceptable salt is dissolved in an aqueous solution. Any suitable means may be used to dissolve the doxycycline or doxycycline salt in the aqueous solution. Generally, all that is required is some form of mixing. The aqueous solution is preferably comprised of at least about 75 wt. % water. Other components can be included in the aqueous solution such as, for example ethanol. The aqueous solution generally will have a pH that is in a range of about 1 to about 8.
Suitable metal salts include but are not limited to, calcium salts, sodium salts, magnesium salts, zinc salts, and mixtures thereof. A particularly preferred metal salt is calcium chloride. The metal salt is added with or without mixing, but it is generally mixed into solution.
About 1 wt. % to about 50 wt. % of the metal salt is added to the aqueous solution, based on the total weight of the doxycycline formulation. Preferably, the metal salt is about 1 wt. % to about 25 wt. %, more preferably 3 wt. % to about 10 wt. %.
A base is added to the aqueous solution and mixed with the other components. The base is added in an amount effective to form a suspension of the doxycycline metal complex. Generally the addition of the base raises the pH of the solution to a pH range of about 2.5 to about 8. Suitable bases include for example, sodium hydroxide, potassium hydroxide, triethanolamine, diethanolamine, monoethanolamine, sodium bicarbonate, and mixtures thereof.
The amount of base that is added will depend on various factors, including the pH of the aqueous solution and the formation of the suspension. Generally, about 1 wt. % to about 5 wt. % of the base is added, based on the total weight of the doxycycline formulation. More preferably about 2 wt. % to about 4 wt. % of the base is added.
Drying the suspension may be carried out using a variety of techniques. For example in one embodiment, a spray dryer is used and the suspension is sprayed onto an excipient. Other methods include decanting, evaporation, freeze drying, tray drying, fluid-bed drying, and the like.
In another embodiment, the process for making a solid dosage form of a doxycycline metal complex comprises the steps of: (i) providing an aqueous solution of doxycycline or a physiologically acceptable salt thereof; (ii) admixing a metal salt with the aqueous solution, (iii) admixing a base to increase the pH of the solution, thereby forming a suspension of doxycycline metal complex; (iv) admixing one or more pharmaceutically acceptable-excipients with the suspension, thereby forming a wet granulation; and (v) drying the wet granulation, thereby forming a dry granulation of the doxycycline metal complex. Steps (i)-(iii) of this embodiment are the same as the prior described process that forms the solid dosage form from the suspension.
This embodiment, however, utilizes an excipient to assist in forming a wet granulation. The inventors have discovered that an excipient, e.g., microcrystalline cellulose, will absorbed and adsorbed the moisture in the suspension when admixed with the suspension. The result is a wet granulation or slurry that has about 5 wt. % to about 99 wt. % water. Preferably, the moisture in the wet granulation is about 25 wt. % to about 60 wt. %. By forming the wet granulation, the drying process can proceed more readily.
One or more pharmaceutically acceptable-excipients can be admixed in either process during any of the process steps. Moreover, excipients can be added in more than one step.
The wet granulation may be drided by tray-drying, fluid-bed drying, decanting, evaporating, freeze drying, a combination thereof, or by other processes known to those skilled in the art.
It is desirable that the doxycycline metal complex granulation be dried to a moisture content of about 1 wt. % to about 15 wt. % based on the total weight of the doxycycline metal complex granulation. More preferably, the moisture content should be less than about 10 wt. %. Most preferably, to about 1 wt. % to about 6 wt. %.
The resulting doxycycline metal complex is in the form of a dry granulation consisting of granules and powder. The dry granulation may be blended with excipients such as lubricants, i.e. magnesium stearate. The final blend may be further processed, by filling it into capsules.
The inventors have also discovered that the doxycycline metal complex granulation formed after the drying step is well suited for tableting. In fact, should the formulator choose, tableting operations may be performed without the use of additional tableting excipients. Another significant advantage is, unlike other synthesis processes, the method of the present invention does not require a purification step to remove undesirable impurities. This makes the process more efficient and enables tablets to be made directly from the doxycycline metal complex granulation. However, it should be understood that tableting excipients may be incorporated. As previously noted, the excipients, i.e. lubricants, may be added before and/or after the step of drying the suspension or wet granulation. The excipients are simply added and mixed with the other components.
In a preferred embodiment, the tablets are chewable tablets. This would be greatly beneficial to those who suffer from esophageal ulceration, since a chewable tablet of a doxycycline metal complex is not soluble in the esophageal environment. Therefore the chewable tablet would pass through the esophagus in a harmless manner.
In addition, the solid dosage form of the present invention may contain additional ingredients. For example, the additional ingredients may include natural and artificial flavors, sweeteners, colorings, coating excipients, binders, disintegrants, lubricants, and the like.
The solid dosage form is generally orally administrated in the form of tablets, capsules, powders, granules, lozenges, aerosols, pellets, chewable tablets, and the like. Excipents such as binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, or polyvinyl-pyrrolidone; fillers for example lactose, sugar, maize-starch, calcium phosphate, sorbitol or glycine; tableting lubricant, for example magnesium stearate, talc, polyethylene glycol or silica; disintegrants for example potato starch, or acceptable wetting agents such as sodium lauryl sulphate, may be included to facilitate the formation of the tablet. In addition, coatings may be applied over the tablets using methods known in the art.
The present invention also includes a method for treating bacterial infections. The method comprises the step of administering to a host, such as a human or animal, a safe and effective amount of a doxycycline metal complex, in solid dosage form. Examples of bacterial infections that can be treated with a doxycycline metal complex, include urinary tract infections, upper respiratory tract infections, acne, gonorrhea, chlamydia, syphilis, anthrax, lyme disease and the like.
The solid dosage form of a doxycycline metal complex may be used in the treatment of ailments caused by bacteria and microorganisms. Non-limiting examples of bacteria and microorganisms are gram-positive microorganisms, gram-negative microorganisms, aerobic bacteria, anaerobic bacteria, spirochetes, mycoplasmas, rickettsiae, chlamydiae, treponema, listeria, bacillus anthracis, fusobacterium fusiforme, actinomyces israelii, clostridium, ureaplasma urealyticum, borrelia recurrentis, haemophilus ducreyi, yersinia pestis, francisella tularensis, vibrio cholerae, brucella, campylobacter fetus, bartonella bacilliformis, calymmatobacterium granulomatis, and protozoans. The treatment would require administering a safe and effective amount of a solid dosage form of a doxycycline metal complex for an effective period of time.
EXAMPLE 1











TABLE 1







Ingredient
% w/w
Total quantity




















Doxycycline hyclate
16.5
830 g



Calcium chloride
5.6
280 g



Sodium hydroxide
2.6
130 g



Microcrystalline cellulose
74.9
3760 g 



Magnesium stearate
0.4
 20 g










A 20-25% solution of doxycycline hyclate is prepared by dissolving 16.5 g of doxycycline hyclate in water. A 50% solution of calcium chloride is also prepared by dissolving 5.6 g of calcium chloride in water. The doxycycline hyclate solution and calcium chloride solution are combined and mixed in accordance with the amounts specified in TABLE 1.
5N Sodium hydroxide is then added to the mixture. This raises the pH of the mixture to about 5. Preferably the pH is raised to about 6, and most preferably, the pH is raised above about 6, but below about 8. This forms a suspension of doxycycline-calcium complex. The doxycycline-calcium complex present in this suspension consists of doxycycline and calcium. The molar ratio of doxycycline to calcium in the complex is 1:1.
An excipient, microcrystalline cellulose (74.9 g), is then added to the suspension. The microcrystalline cellulose absorbs and adsorbs the moisture in the suspension, resulting in the formation of a wet granulation.
The wet granulation is dried using a fluid-bed or tray dryer to reduce the moisture content to less than 10%, and preferably to between about 1% to about 6%, thereby forming a dry granulation.
The dry granulation is milled through a 14-mesh screen.
0.4 g of magnesium stearate is added as a lubricant, to form the final dry granulation.
At this point, a colorant can be added.
The dry granulation can now be used to fill gelatin capsules, or it can be compressed into tablets.
Once the gelatin capsules or tablets are made, a film coating can be applied over the tablets.
EXAMPLE 2











TABLE 2







Ingredient
% w/w
Total quantity




















Doxycycline hyclate
19.3
2480 g 



Calcium chloride
6.5
840 g



Sodium hydroxide
3.0
380 g



Microcrystalline cellulose
71.0
9120 g 



Magnesium stearate
0.2
 30 g










The procedure of EXAMPLE 1 was followed with the exception that the percent by weight of each ingredient was varied as indicated in TABLE 2 above. As in EXAMPLE 1, the doxycycline-calcium complex present in the suspension of EXAMPLE 2 consists of doxycycline and calcium. The molar ratio of doxycycline to calcium in the complex is 1:1.
While the invention has been described above with reference to specific embodiments thereof, it is apparent that many changes, modifications, and variations can be made without departing from the inventive concept disclosed herein. Accordingly, it is intended to embrace all such changes, modifications, and variations that fall within the spirit and broad scope of the appended claims. All patent applications, patents, and other publications cited herein are incorporated by reference in their entirety.

## Claims

1. A solid dosage form comprising a doxycycline calcium complex for pharmaceutical administration, wherein the complex consists of doxycycline and calcium, and wherein the molar ratio of doxycycline to calcium in the complex is 1:1.

2. The solid dosage form of claim 1, wherein said solid dosage form is selected from the group consisting of powders, granules, tablets, coated tablets, gelatin filled capsules, pellets, and chewable tablets.

3. The solid dosage form of claim 2, wherein said solid dosage form is a chewable tablet.

4. A solid pharmaceutical dosage form comprising:
(i) a doxycycline calcium complex, wherein the complex consists of doxycycline and calcium in a solid form, and wherein the molar ratio of doxycycline to calcium in the complex is 1:1; and
(ii) one or more pharmaceutically acceptable excipients.

5. The composition of claim 4, wherein said pharmaceutically acceptable excipient is selected from the group consisting of polymers, resins, plasticizers, fillers, lubricants, binders, disintegrants, granulating agents, solvents, co-solvents, surfactants, preservatives, sweetening agents, flavoring agents, buffering systems, antioxidants, pharmaceutical-grade dyes, pigments, and mixtures thereof.

6. The composition of claim 4, wherein said pharmaceutically acceptable excipient is microcrystalline cellulose.

7. A solid dosage form comprising a doxycycline calcium complex, wherein the complex consists of doxycycline and calcium, wherein the molar ratio of doxycycline to calcium in the complex is 1:1, and wherein the complex was made by a process comprising the steps of:
(i) providing an aqueous solution of doxycycline or a physiologically acceptable salt thereof;
(ii) admixing a calcium salt with the aqueous solution;
(iii) admixing a base to increase the pH of the aqueous solution, thereby forming a suspension of doxycycline calcium complex; and
(iv) drying the suspension, thereby forming a dry granulation of doxycycline calcium complex.

8. A method of treating a bacterial infection in a subject, the method  comprising:
administering to the subject a solid pharmaceutical dosage form comprising a solid doxycycline calcium complex, wherein the complex consists of doxycycline and calcium, and wherein the molar ratio of doxycycline to calcium in the complex is 1:1.